Studies of uterine secretions and products of primary cultures of endometrial cells in pigs.

The uterus plays a central role in the reproductive biology of mammals. Adaptation of the uterus from an oviparous to a viviparous nature required changes that involved production of a uterine environment that could support the development of the embryo and fetus. Production of a suitable environment includes the synthesis and secretion of products by the uterine endometrium. However, the uterine endometrium is not a single homogeneous unit, but rather consists of several cell populations. Recent accomplishments in cell culture techniques provide a means for examining the contributions and secretory control of different endometrial cell populations. Furthermore, it is possible to recombine specific cell types to study their interaction. It is clear that the luminal epithelium, glandular epithelium and endometrial stroma produce different secretory products. Some secretions (for example uteroferrin) are secreted by only one cell type; others (for example prostaglandins, PGs) are secreted by all types of cell. There is much to be learned about the functions and regulations of endometrial secretions and there are important aspects of the role of the endometrium in pregnancy that present concepts do not address. For example, there is no explanation for the required synchrony between the embryo and uterus before day 10 and the implications of control of the uterine environment by progesterone from day 4 to day 10 are not understood. Almost all of the uterine secretory proteins are produced after day 10. In this review, we consider the protein and prostaglandin products from the different cell populations of the pig endometrium and propose a model to explain the integration of multiple sources of PGs and multiple regulators of PG secretion. Our purpose is to facilitate a more complete understanding of the individual uterine cell populations and a better understanding of how these cell types interact to function as a complete unit.